1. Field of the Invention
This invention relates to an interface assembly in a power tongs for selectively disenabling a manually operable valve and for enabling an electrically responsive valve.
2. Description of the Prior Art
Manually operable power tongs to effect the making and breaking of joints between elements of a drill string are known in the art. The tongs manual control console usually is provided with four levers, each of which controls a pilot valve of a small four-section stack valve. Each pilot valve controls one main function of the commonly utilized tongs structure.
For example, one valve controls the opening and closing of the backup tong. A second valve controls the tongs motor to rotate the power driven tong. The lift speed of the tongs is controlled by a third valve, while a fourth valve controls the upward or downward movement of the tongs lift. Of course, other tongs functions as, for example, the extension of the stabber (if one is provided) or the extension of a joint sensor would require a manual valve for the operation of each.
It would be advantageous to automatically control a power tongs arrangement by utilization of an electrical tongs control system. However, if an electrical control system is utilized, it is necessary to provide a suitable electro-hydraulic interface to permit valves which are manually operable to be operable in response to electrical signals output from the control system. To locate the power driven and backup tong in a predetermined operating relationship with respect to the tool joint, a joint sensor arrangement is advantageously utilized.